Preheat the oven to 350ºF. Line a baking sheet with parchment paper or a silpat liner. (Or lightly grease the baking sheet.)

In a large bowl or the bowl of a stand mixer, beat the butter until it is smooth. Add the sugar, vegetable oil, sour cream, egg yolks, and vanilla extract. Mix until combined.

In another bowl, mix together the flour, cocoa powder, baking powder and salt until completely combined. Add the dry ingredients all at once to the wet ingredients and mix just until combined.

Using a 3 tablespoon scoop, scoop the dough onto the baking sheet, leaving at least 2 inches between each cookie.

Bake the cookies for 5 minutes. With a flat spatula, press the cookies down slightly to make them about 1/2” thick. Return to the oven and bake for an additional 5 minutes. Remove from the oven and let cool on the baking sheet for 5 minutes, then remove to a sheet of waxed paper to cool completely.

To make the frosting, beat the butter until light and fluffy. Beat in the vanilla and salt. Start adding in the powdered sugar, 1/2 cup at a time. Add the milk as needed to make the frosting a spreadable consistency. If desired, add in some red food coloring to make the frosting pink.